Existing aircraft landing systems, such as the present Microwave Landing System (MLS) as specified by international agreement, enable an aircraft preparing to land at an airport to derive data representative of aircraft location relative to the desired flight path to a runway. In such systems, ground-based antennas transmit a vertically-oriented fan beam which is scanned back and forth horizontally and a horizontally-oriented beam which is scanned up and down vertically. An aircraft flying through these cross-scanned beams carries a receiver capable of determining the time of incidence of the beams at the location of the aircraft. Data on such time of incidence is then used with data as to the timing of the scanning of the cross-scanned beams to derive information relating to the aircraft location relative to the runway or desired flight path.
In considering development of an aircraft landing system suitable for use by aircraft landing on an aircraft carrier, it was determined that additional constraints, such as caused by multipath sea reflection effects in the presence of roll and pitch conditions, limited the effectiveness of existing MLS capabilities. In addition to the fact that aircraft positional data may require correction to compensate for roll and pitch of the aircraft carrier, MLS system performance was determined to be subject to severe degradation of azimuth accuracy resulting from multipath reflections of signals from the surface of the water between the ship and an aircraft preparing to land, particularly in the presence of roll and pitch.
It is therefore an object of this invention to provide aircraft location systems having new and improved capabilities and, more particularly, to provide X-scan systems suitable for use in aircraft landing operations on aircraft carriers and such systems capable of operation in the presence of varying multipath reflections from the surface of the sea.
Further objects are to provide new and improved linear array antenna systems and methods operating with vertically aligned radiating elements to provide diagonally oriented fan beams which are scanned to provide horizontal coverage.
Additional objects are to provide diagonal fan beam antennas which can be constructed using sections of standard waveguide for wide band operation, and new and improved systems and methods which avoid disadvantages or shortcomings of the prior art.